util: remove unused function virFirewallApplyRuleFirewallD()
This was a wrapper to call a function in virfirewalld.c that sends an
iptables passthrough rule to firewalld. It hasn't been used in a year
or two, and won't ever be used in the future since passthrough rules
are only supported for iptables, and we've determined that we
shouldn't use iptables passthrough rules.
Signed-off-by: Laine Stump <laine@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>